The PAVN plan called for the platoon from the 10th Sapper Battalion to infiltrate the city on the evening of 30/31 January to pave the way for a major assault by elements of the 812th Regiment.

Commandos from the 10th Sapper Battalion would also attack Landing Zone Jane south of La Vang to keep the American forces there tied down.

In the weeks before Tet, they had attempted to lure Allied forces from the coastal lowlands to the mountains by threatening several of the Marine combat bases along Highway 9 in the western part of the province.

But while the U.S. Marines had shifted some forces to the besieged Khe Sanh Combat Base, MACV commanders had reinforced eastern Quảng Trị Province in late January with the 1st Brigade of the 1st Cavalry Division.

The existence of major American units near Quảng Trị City came as a shock, but with little time to make adjustments, the Communists decided to move forward with their original plan.

These were the 1st Vietnamese Regiment, the 9th Airborne Battalion, an Armored Personnel Carrier (APC) Troop attached to the 1st Regiment (2nd Troop of the ARVN 7th Cavalry), the Republic of Vietnam National Police headquarters in the city, a military body similar to the French Gendarmerie led by regular military officers, and Regional and Popular Force (militia) elements in the city.

[2] As the 814th Battalion was moving into position to attack Quảng Trị from the northeast, it unexpectedly encountered the 9th ARVN Airborne company in Tri Buu village, which engaged it in a sharp firefight lasting about 20 minutes.

The Airborne company was nearly annihilated and an American adviser killed, but its stubborn resistance stalled the 814th battalion's assault on the Citadel and the city.

South Vietnamese irregulars and National Policemen slowed the enemy’s advance, however, and its assaults on the southern wall of the Citadel were beaten back.

At about the same time, ARVN troops at La Vang began moving north toward the fighting between the Airborne companies and the K6 Battalion in the cemetery south of the city, and were ambushed by the K6th, slowing their advance to a crawl, and they were unable to relieve the paratroopers.

Only the K5 Battalion, holding its position in Hai Lang District well south of the city to block reinforcements from Huế, remained unengaged in the fighting.

The 1st Battalion, 502nd Infantry Regiment, which was under the control of the 1st Cavalry Division, continued its base defense mission and patrols west of Quảng Trị.

At approximately 13:45 on 31 January, Col. Rattan directed the battalions to close out the new fire bases and launch assaults as soon as possible to prevent the PAVN/VC from bringing additional forces into the city and also blocking their withdrawal.

[2]: 55 Two companies of the 1/5th Cavalry air-assaulted southeast of Quảng Trị engaging the K6 Battalion from the rear in a heavy firefight, while ARVN troops blocked and attacked it from the direction of the city.

They attributed the decisive defeat to the hard-nosed South Vietnamese defense, effective intelligence on PAVN/VC movements provided by Robert Brewer, and the air mobile tactics of the 1st Cavalry Division.

[2]: 57 The rapid defeat of the regimental-size enemy force that assaulted Quảng Trị City proved to be one of the most decisive victories the Allies secured during the Tet Offensive.

The PAVN/VC's swift defeat preserved an important symbol of South Vietnamese national pride and allowed the allies to devote more resources to other battles in northern I Corps, particularly to the struggle for Huế.